Nematic Liquid Crystal Panel Research Articles

75‐3: Highly Collimated Backlight for Liquid Crystal Displays

In this work, we present the design of a collimated backlight design that can be used for a liquid crystal display. The design is based on a hexagonal array of white light emitting diodes (LEDs) in combination with two arrays of lenses. Ray tracing simulations show a full width ‐ half maximum (FWHM) collimation angle of 2.8º with a uniformity of 73%. A prototype of this design has been fabricated and its performance has been analyzed. Compared to a standard backlight, the collimated backlight provides a 4.2 times better contrast ratio for a twisted nematic (TN) liquid crystal (LC) panel. In combination with a diffusor in front of the LC panel, the contrast ratio under a wide viewing angle is improved by a factor of 10 and the color shift is reduced by 79%.

Design of retinal-projection-based near-eye display with contact lens.

We propose a design of a retinal-projection-based near-eye display for achieving ultra-large field of view, vision correction, and occlusion. Our solution is highlighted by a contact lens combo, a transparent organic light-emitting diode panel, and a twisted nematic liquid crystal panel. Its design rules are set forth in detail, followed by the results and discussion regarding the field of view, angular resolution, modulation transfer function, contrast ratio, distortion, and simulated imaging.

25‐1: Invited Paper: Improvement of Viewing Angle and Color Gamut of Twisted Nematic Liquid Crystal Display using Inkjet‐printed Quantum Rod Color Pixel Converter

Quantum rod‐based color conversion subpixels were fabricated by ink jet printing and stacked on a twisted nematic liquid crystal panel to improve its viewing angle and color gamut. The panel covers 80% of the BT.2020 standard color gamut, and the resulting color conversion layer produced a very wide viewing angle.

Polarized light-emitting backlight unit using a retardation film for improving light efficiency in a twisted nematic mode liquid crystal module

We propose and demonstrate a new polarized backlight unit (BLU) configuration to enhance light transmission in a twisted nematic (TN) mode liquid crystal (LC) panel. By adding an optimized phase retardation film (PRF) to the BLU, we efficiently controlled the polarization state of the light from the light guide plate (LGP), enabling it to be aligned along the transmission axis of the bottom polarizer of the LC panel. We designed and fabricated a 7 in. edge-lit BLU with a PRF. To obtain a uniform positional distribution in both light intensity and degree of polarization (DOP), the LGP was optimized with linear groove patterns. To maximize BLU light transmission through the bottom polarizer in a TN-mode LC panel, the slow axis of the PRF was aligned at 22.5° with respect to the LED array axis. We improved the transmittance from 45 to 72%.

Polarimetric Measurement of Jones Matrix of a Twisted Nematic Liquid Crystal Spatial Light Modulator

A polarimetric experimental method was developed to determine the Jones matrix elements of transparent optical materials without sign ambiguity. A set of polarization dependent transmittance data of the samples was measured with polarizer - sample - analyzer system and another set of data was measured with polarizer - sample - quarter-wave plate - analyzer. Two data sets were compared and mathematically analyzed to obtain the correct signs of the elements of the matrix. The Jones matrix elements of a quarter-wave plate were determined to check the validity of the method. The experimentally obtained matrix elements of the quarter-wave plate were consistent with the theoretical expectations. The same method was applied to obtain the Jones matrix elements of a twisted nematic liquid crystal panel.

Influence of grating period on kinetics of self-diffraction in nematic liquid crystal panel with photoconducting polymeric layer

The authors report on grating spacing influence on self-diffraction phenomenon in nematic liquid crystal panel with photoconducting polymeric layer. For grating recording typical degenerated two-wave mixing experimental set-up was used. Self-diffraction was induced by neodymium doped yttrium aluminum garnet laser (Nd:YAG, λ=532 nm) and for the observation of temporal changes of diffraction efficiency in function of grating period (angle between two recording beams coming from the Nd:YAG laser) laser diode (λ=674) was used. Mathematical model for grating formation based on coupling of three gratings was proposed. Theoretical estimations and experimental results have shown very good agreement.

Study of self-diffraction phenomenon in hybrid liquid crystal panel

In this paper we present the results of dynamics of hologram generation in hybrid nematic liquid crystal panels with photoconducting layers (made of poly-N-vinyl-carbazole doped with 2,4,7-tri-nitrofluorenone) for different applied voltages. During experiments we have measured the temporal changes in the diffraction efficiency coefficient. To reach the equilibrium between all writing processes we have used the ‘long pulse method’ to generate holograms. This method exhibited the insufficiency of earlier presented refractive index time dependence and a new model had to be proposed. We assumed the existence of charge traps in photoconducting layers which results in additional erasing functions in particular refractive index time dependence. Comparison of the newly proposed mathematical model and the experimental results has shown very good agreement.

Enhancement of Contrast Ratio by Using Ferroelectric Nanoparticles in the Alignment Layer of Liquid Crystal Display

We demonstrate the effect of the ferroelectric nanoparticles dispersed in the alignment layer of a twisted nematic (TN) liquid crystal (LC) panel. In comparison to a conventional TN LC panel with a conventional polymide layer, the TN LC panel with an alignment layer doped with ferroelectric nanoparticles shows a much higher contrast ratio. The effects of barium titanate nanoparticles at several different concentrations have been studied, among which 2.5 and 5 wt % barium titanate nanoparticles mixtures show better performances. The surface texture of the alignment layers has also been studied by atomic force microscopy (AFM).

TFT를 이용한 비틀린 네마틱 액정 셀에서 외부 압력에 따른 액정 동력학에 관한 연구

We have studied the pressure-dependent liquid crystal's dynamics in a twisted nematic (TN) liquid crystal panel with thin film transistor by applying an external pressure to it. When the external pressure is applied to the panel in a dark state, the disclination lines were generated as a light leakage whereas they did not appear in a simple test cell that has only pixel and common electrodes. It was because the disclination lines were Provoked by the electric field between pixel electrode and data/gate bus line for active matrix driving. Consequently, the external pressure resulted in dynamic instability of the liquid crystal so that the disclination lines at the data/gate bus line intruded into the active area.

Electro-optic phenomena in nematic liquid crystals studied experimentally and by Monte-Carlo simulations

In this article we compare results of experiments on light self-diffraction in nematic liquid crystal panels with corresponding results of the Monte-Carlo simulations of a two-dimensional nematic liquid crystal model in the presence of a spatially modulated electric field. In the simulations molecular interactions were described by the Lebwohl–Lasher Hamiltonian. The results obtained on the diffraction efficiency and spatial and temporal behavior of refractive index changes in nematic liquid crystal are satisfactorily reproduced by Monte-Carlo simulations. We discuss the complementarity of both methods in studying and designing systems for optical information processing using liquid crystals.

Nematic Liquid Crystals as Media for Real-Time Holography

We report on a novel type of orientational photorefractive devices consisting of dye-doped or pure nematic liquid crystals. These systems can be employed as the recording media for real-time (dynamic) holography. Optical addressing of liquid crystal molecules is facilitated due to the natural tendency of molecular self-assembling in nematics and their easy reorientation upon action of an electric field. This field can be produced by incoming light via photoconductivity either in the bulk or at the surface of the nematic liquid crystal layer. We present an experimental study of dynamic self-diffraction of light on thin phase holograms formed in a nematic liquid crystal panel. Optically addressed spatial light modulators designed by us can be the active elements of image processing systems and in this communication we demonstrate the optical correlator performing image recognition.

Genetic optimization of modulation characteristics for two twisted nematic liquid crystal spatial light modulators

A single twisted nematic liquid crystal spatial light modulator may suffer from coupled amplitude modulation and a phase modulation capability of less than 2π, although almost all panels can achieve π. Two twisted nematic liquid crystal panels can be combined in an optical system to produce a total phase modulation of at least 2π, and a minimal coupled amplitude modulation. A genetic algorithm is used to optimize the combined modulation characteristics of two liquid crystal panels in a multiplicative architecture. Simulation results and experimental verification are presented which show a substantial reduction in the combined amplitude modulation, and a total phase modulation of 2π.

Calculations of Electric Field Dependence of Effective Refractive Index in Nematic Liquid Crystal Panel

Novel approach to calculation of changes of extraordinary effective index of refraction upon action of an external electric field for a case of a homogeneous nematic is presented. The solution of the static sine-Gordon equation, even for the simplest case (symmetrical hard boundary conditions, one elastic constant approximation within Ericksen — Lesile theory) requires an use of Jacobian elliptic functions. The numerical calculations based on the presented solutions agree well with the experimental data.

Phase-Only Modulation with a Twisted Nematic Liquid Crystal Panel for a Reconfigurable Grating

A single-path transmission type twisted nematic liquid crystal panel appears to achieve nearly phase-only spatial light modulation when placed between a properly aligned polarizer and analyzer. We obtained more than π phase delay with the equipment whose retardation was less than π.

Optimization of twisted nematic liquid crystal panels for spatial light phase modulation

To optimize a twisted nematic liquid crystal panel for large phase modulation, it is necessary to optimize the angles of the polarizer and analyzer. We determine the Jones matrix of a panel and find these optimum angles by computer simulations. They compare well to the experimental results.

Phase Modulation Capability of Thin Twisted Nematic Liquid Crystal Panels at Double-Pass Configurations

Spatial light modulators whose phase modulation capability (PMC) exceeds 2π are strongly desirable. A double-pass configuration was evaluated to enhance PMC of twisted nematic liquid crystal panels. Theoretical analysis using Jones calculus is given, and it is proved that phase modulation is exactly doubled when the panel is sandwiched by two polarizers. Experiments to measure the PMC were carried out and results coincide well with the theory.

Fast and Accurate Phase Retardation Measurement of 0° Twisted Nematic Liquid Crystal Panels Based on the Principle of Homodyne Receiving

We describe herein a method to measure quickly (in less than 2 min) and accurately the phase retardation between the extraordinary and ordinary axis of homogeneous or 0° twisted nematic liquid crystal panels. Owing to the homodyne detection scheme, the setup allows us to probe liquid crystal (LC) panels with an optical power down to a fraction of 1 nW and, hence makes it possible to focus the light beam to a spot of only a few wavelengths in diameter without heating or inducing observable variations in the liquid crystal. The dependence of the phase retardation on the LC driver frequency and the temperature are presented and compared with the theoretical prediction.

Multicolor LCD for automotive applications

Segment-type, twisted nematic liquid-crystal panels with finely striped, two-color filters within the panel are discussed. The panel has a color filter-on-indium tin oxide structure. Two types of printed filter (an offset-printed (OP) filter and a screen-printed (SP) filter) were subjected to heat treatment and evaluated. It was found that an SP filter of about 0.3 mu m has less effect on the operating voltage and availability for multiplexed drive than an OP filter of about 1 mu m in thickness with the same color density. The test results for panel reliability for automotive use are given. The panels can digitally display a vehicle's speed, fuel level and engine revolutions in bargraph format with good legibility using three colors. >